In a lightly greased saucepan, saute onion and garlic for about 5 minutes until tender. Stir in flour, cook over medium heat 2 minutes, stirring frequently.

Add squash and broth to saucepan; heat to boiling. Reduce heat and simmer, covered, until squash is tender, 15 to 20 minutes.

In a blender or food processor, process soup until smooth; season to taste with salt and white pepper. Serve warm, or chilled. Drizzle each bowl of soup with Cilantro Sour Cream and sprinkle with cilantro.